1. Field of the Invention
The invention relates generally to a method of storage and utilization of heat energy and, in particular, the use of a low temperature reversible, controllable chemical dissociation and recombination reactions to provide a solar energy storage system.
2. Description of the Prior Art
The rapid depletion of conventional natural sources of energy is causing increasing national alarm over the probability of a severe energy crunch in the near future. This has lead to a recent technology explosion related to the exploitation of the use of solar energy as an alternative source to meet our ever-increasing energy needs. Solar energy is becoming important as a necessary alternative to such natural energy sources as petroleum and natural gas especially in the field of heating and cooling buildings and the generation of electrical power.
One of the problems associated with the utilization of solar energy in the heating and cooling of buildings and other low temperature applications utilizing such energy in the form of heat lies in the difficulty of storing heat extracted from solar collectors and the like for later use. Prior art attempts to achieve a practical method of storage of such heat energy include physical methods such as utilizing storage materials having high heat content or taking advantage of the heat of fusion or vaporization of materials. Additionally, the use of chemical reactions to store such heat for later use has been proposed.
One such prior art system is disclosed in a patent to Sasse, et al. U.S. Pat. No. 3,994,675 issued Nov. 30, 1976 in which certain compounds such as substituted naphthalenes are employed which undergo reversible endothermic photochemical reactions to form other compounds which can later be exothermically reverted to the original naphthalenes with the release of heat. That disclosure, of course, would require the actual reaction to take place in the presence of the solar energy. Another such reference is contained in a patent to Curtis U.S. Pat. No. 3,598,103 issued Aug. 10, 1971 in which an underwater heating system for a swimmer utilizes the heat of solution of ammonia in water to maintain the temperature of a swimmer's diving suit or underwater chamber at a comfortable level.
Additional prior art patents which utilize reversible chemical reactions to store energy chemically include U.S. Pat. No. 3,958,625 to Wentorf issued May 25, 1976 which discloses a method to absorb heat from a nuclear reactor by endothermically reacting carbon dioxide (CO.sub.2) and methane (CH.sub.4) to form a mixture of carbon monoxide (CO) and hydrogen (H.sub.2). The CO and H.sub.2 are subsequently reacted exothermically to reform CH.sub.4 and CO.sub.2 and the heat evolved utilized for other purposes in a relatively high temperature system. Another such process is illustrated and described in U.S. Pat. No. 3,967,676 to Spacil issued July 6, 1976 which reveals a process which also may be used in cooling nuclear reactors. That reference involves endothermically dissociating phosgene (COCl.sub.2) to form carbon monoxide (CO) and chorine (Cl.sub.2) and subsequently exothermically reacting the CO and Cl.sub.2 to reform COCl.sub.2. That system is also designated to operate in the higher temperature range of 400.degree. to 500.degree. C.
Of the above prior art energy storage use applications, those involving reversible chemical reactions appear to provide more practical means of energy storage and reconversion. While each of these may be used successfully in certain environments, each also suffers from certain drawbacks for relatively low-temperature applications. Thus, certain of the prior art chemical heat storage and utilization systems involving reversible reactions require relatively high temperatures or contain highly toxic substances as evidenced by the use of carbon monoxide and phosgene.